1. Field of Invention
The invention relates to a heat insulating container having a double-wall structure and a manufacture method therefor. More specifically, the invention relates to a heat insulating container that includes an inner glass container and an outer glass container with a gap formed in-between.
2. Description of Related Art
A heat insulating container comprising an inner glass container and an outer glass container, such as a vacuum flask, has been in common use. The heat insulating container has a structure comprising an inner glass container housed in an outer glass container with a gap formed in-between. In such a heat insulating container, the gap is in a vacuum, or a low-thermal-conductivity gas (for example, argon, krypton or xenon) having a thermal conductivity lower than that of air is sealed within the gap, so that the gap can serve as a heat insulating layer. Furthermore, in this type of heat insulating container, a radiant heat preventive film is usually formed on the outer surface of the inner container or the inner surface of the outer container by utilizing a silver mirror reaction or the like.
To manufacture the above heat insulating container, for example, the following method may be adopted. The inner container and the outer container are integrally joined together at the ends of the container opening. Next, a silver-containing solution is injected into the gap such that the silver-containing solution gets adhered to predetermined surfaces of the inner and the outer containers. Next, the resulting structure is heated at a temperature of about 200° C. to dry the silver-containing solution and thereby form a silver film. Subsequently, the gap is made vacuum by exhausting the gap of air through a tip tube provided on the outer glass container. Otherwise, a low-thermal-conductivity gas is sealed within the gap. In both cases, the gap is transformed into a heat insulating layer.
Japanese Patent Application Laid Open Publication No. 2001-505088 discloses a heat insulating container, in which a radiant heat preventive film made of metal oxide (SnO2, In2O3, ZnO, etc.) with a resistivity of 10−4 Ω·cm or less is formed on the surfaces of the inner container and the outer container. The heat insulating container disclosed in the above publication has an advantage that the contents of the container can be seen because the radiant heat preventive film is highly transparent.
However, a radiant heat preventive film formed from a metal oxide usually has a low performance in preventing radiant heat because of the restrictions of the manufacturing conditions. Therefore, it is difficult to produce a heat insulating container that is excellent in heat insulating capability.